Noninductive resistor especially adapted for high - frequency power



Feb. 28, 1950 Filed Aug. 21, 1946 INVENTORS rmuhwz ATTORNEY Patented Feb. 28, 1950 NONINDUCTIVE RESISTOR ESPECIALLY HIGH FREQUENCY ADAPTED FOR POWER Norman C. Fulmer and Julian J. Mason, Montclair, N. J., asslgnors to Westinghouse Electric CorporatiomEast Pittsburgh, Pa, a corporation of Pennsylvania Application August 21, 1946, Serial No. 692,688

13 Claims. ll

This invention relates to resistors and in particular to such having low values of inductance and capacitance, whereby they are particularly adapted for high-frequency applications.

The principal object of our invention, generally considered, is to produce resistors especially adapted for frequencies to several megacycles, and having low values of distributed inductance and capacitance.

Another object of our invention is to produce resistors each comprising a plurality of sections of thin layers of resistance material, so arranged that mutual cancellation of self-induced fields reduces the effective inductance to a negligible quantity.

A further object of our invention is to produce resistors having hollow cylindrical portions formed with thin walls in order to reduce the skin-effect, and so connected that when in use current in adjacent portions flows in opposite directions to approximately cancel self-induced fields, the terminals being widely spaced to reduce capacitance.

Other objects and advantages of the invention, relating to the particular arrangement and corn struction of the various parts, will become apparent as the description proceeds.

Referring to the drawing:

Figure l is an axial sectional view, with parts in elevation, illustrating one embodiment of our invention.

Figure 2 is a fragmentary sectional view showing the upper left-hand corner of the resistor of Figure 1 to a larger scale.

Figure 3 is a fragmentary sectional view, cone spending to Figure 2, but showing a modification.

Figure 4 is a transverse sectional view on the line IVIV of Figure 1, in the direction of the arrows.

Figure 5 is a view corresponding to Figure i showing another embodiment.

Figure 6 is a perspective view of another em. bodiment of our invention.

For many applications, especially in highfrequencycircuits, it is essential that resistors have low values of distributed inductance and capacitance. In accordance with our invention, we have produced a type of non-inductive resistor composed of a plurality of sections of thin layers of resistance material, so arranged that a mutual cancellation of self-induced fields reduces the effective inductance to a negligible quantity.

erably of large diameter and short length. A serious objection, however, to the use of such a resister at high frequencies, is the apparent increase in resistance as the frequency increases. Such increase in resistance is due to what is called skin-effect," as high-frequency current tends to be concentrated in the outer periphery or skin of the resistor, thereby decreasing the efiective cross-sectional area. Because of skineifect it is sometimes preferable to construct high-frequency resistors in the form of holiow thin-walled or sheet cylinders in order to provide more constant resistance over a wider range of frequency. A common method of making such a resistor is to apply a suspension of carbon to an insulating cylinder when the suspension dries, a thin layer of carbon remains, forming the resistance element.

Referring to the drawing in detail, like parts being designated by like reference characters, and first considering the embodiment of our invention illustrated in Figures 1, 2, and 4, there is shown an insulating cylinder H, which may be hollow or solid, but is preferably hollow, coated with a sheet or film of resistance material l2, preferably from a suspension of carbon or graphite. Narrow bands l3 of sheet or film conductive material, preferably silver, are painted, sprayed, or plated on the resistance material l2 at equal intervals, as shown. Connections to the conductive bands ii: are made by conductive straps l4, l5, l8, H, and Hi. The straps are preferably silver-plated copper which are clamped around the conductive bands.

Alternate conductive straps are connected together by conductive bars I? and it, as shown, said bars forming the two terminals of the resistor. These bars are connected to the straps in any desired manner, as by soldering, welding, or the use of bolts 22 and nuts 23, as illustrate-: In stead of using conductive straps, the conductive bar terminals could be soldered, brazed, or otherwise electrically connected to the conductive manner, as by soldering, brazing or welding 36.

The "simplest type of resistor construction which provides a fairly low value of inductance, is

a straight homogeneous resistance element, pref- The straps I l and is are shown extending for support to the member 24, with their ends bent outward, as indicated in 21 and 2B, and secured there by bolts 29 and nuts 3 I. The shield member 24, therefore, serves as a terminal and may be grounded as indicated at 32. A lead 33 from the bar terminal l9 extends out through an aperture 34' in said member.

Referring now to the embodiment of our-invention illustrated in Figure 3, there is shown a form of resistor like that of Figures 1, 2, and 4, except that the conductive straps, only one of which, 14, is illustrated, are applied first to the insulating cylinder II, and then the resistance material i2 is applied thereover. Except as specifically described, the present embodiment may correspond with the first embodiment.

Referring now to the embodiment of our invention illustrated in Figure 5, there is shown an insulating cylinder H coated with a resistance material l 2', preferably from a suspension of carbon or graphite, as in the previous embodiment. Narrow bands I3 of conductive material, preferably silver, are applied on the resistance material at equal intervals, as heretofore. Connections to the conductive bands are made by conductive straps l4", l5 I6, N and a final strap corresponding with the strap [8 of the first embodiment, not shown. The straps are preferably silver-plated copper, which are clamped around the conductive bands.

Alternate conductive straps are connected together by conductive bars I9 and 2!", as shown, said bars forming two terminals of a resistor, and having leads 21 and 33 respectively, in the enclosing hollow metal cylindrical member 24. The leads 21 and 33 may be connected to the respective bars 2 I and l9 in any desired manner, as by being threaded and fitting correspondingly threaded pockets and/or by solderingor welding. As an alternative, the conductive bars l9 and 2 l could be soldered, brazed, or otherwise electrically connected to the conductive bands l3 instead of to the straps.

In the present embodiment, the resistor is supported by having its insulatin cylinder Ii extended beyond the ends of the member 24 and fitting corresponding inwardly opening pockets 35 in the circular metal plates which close the ends of member 24 like the plates 25 and 26 close the ends of member 24 of the first embodiment. Said plates, only one of which is illustrated, are connected to the member 24 in any desired manner, as by soldering, brazing or welding 36 Referring now to the embodiment of our invention illustrated in Figure 6, there is shown an insulating cylinder ll, coated with a resistance material l2 preferably, from a suspension of carbon or graphite. An even number of narrow strips 43 of conductive material, preferably silver, are applied to the resistance material i2 at equal circumferential intervals, as shown, parallel to the axis of the cylinder.

Terminals of the resistor are conductive rings 31 and 38, and electrical connections are made from each ring to alternate conductive strips l3 on the resistance material |2. That is, conductive plates or bars 39 extend from the conductive ring 31 to every other conductive strip i3, and conductive plates or bars 4! extend from the remaining conductive strips to the ring 38. The conductive bars 39. and 4|, which are preferably silver-plated copper, may be connected to the resistance elements or the conductive strips thereon by soldering, brazing, welding, or by means of an insulative clamp, not shown, around the outside periphery of the resistor. The resistor. may be 4 enclosed in a hollow cylindrical conductive shield member like that designated 24 in Figure 5, with the leads 2'! and 33 passing out through the sides or ends thereof, as desired.

As an alternative, the bars 39 and 4| may be inset in the outer surface of the cylinder H, as illustrated, the bottoms and sides of the receiving grooves, as well as the outer surface of the cylinder, carrying the resistance coating. The conductive material 13 may be applied in the grooves prior to insetting the bars 39 and ti, or the bars may be first inset and the resistance material I2 then applied to the cylinder H and outer surface of the bars.

Arrows have been applied to the drawings to indicate the relative directions of the current flow in the embodiments illustrated. It will thus be seen that current flows in opposite directions in adjacent sections. Thus inductive fields set up by the current in adjacent sections will be of opposite polarity, and neutralize one another with a tendency toward cancellation. The resistors, therefore, have low inductance because of the mutual cancellation, from a practical standpoint, of any self-induced fields, and because the current path is short and of large cross-sectional area. Capacitance is low because of the generous spacing between terminals. The resistance is little affected by frequency because the current path is a large diameter shell.

Any number of resistance elements may be used. Four of these are shown in the embodiments of Figures 1 and 5. The inductance should be the lowest when the resistor consists of several short resistance elements. The total resistance of the embodiments of Figures 1 and 5 may be computed by the following formula:

where R=total resistance in ohms,

=resistivity in ohms per inch square of the resistance coating,

l=length in inches of each resistance section,

d=diameter in inches of the resistance coating and,

n=number of resistance sections.

An advantage of the construction illustrated in where R=total resistance in ohms,

=resistivity in ohms per inch square of the resistance coating,

d==diameter in inches of the resistance coating,

n=number of resistance sections=number of contact strips,

w=width of a single contact strip, and

Z=length of the cylindrical resistance coating.

Although preferred embodiments of our invention have been disclosed, it will be understood that modifications may be made within the spirit and scope of the appended claims.

We claim:

1. A resistor comprising an insulative support, a plurality of coplanar resistance elements as coatings thereon, and leads connecrting said coatings in parallel so that when in use the current in adjacent coatings flows in opposite directions to cancel self-induced fields.

2. A resistor comprising an insulative support, a plurality of coplanar carbon films carried thereby, and leads connecting them in parallel to widely-spaced terminals, so that when in use the current in adjacent films fiows in opposite directions to cancel self-induced fields and the capacitance is low because of the terminal spacing.

3. A resistor comprising an insulating cylinder, plurality of thin-walled coplanar hollow sheet resistance elements mounted thereon, and leads connecting them in parallel, so that when in use the current in adjacent elements flows in opposite directions to cancel self-induced fields.

4. A resistor comprising an insulative support, a plurality of thin-walled coaxial sheet resistance elements carried thereby, and leads connecting them in parallel, so that when in use the current in adjacent elements flows in opposite directions to effect neutralization of self-induced fields.

5. A resistor of low inductance and capacitance, comprising a plurality of thin-walled coaxial hollow cylindrical resistance elements, and leads connecting them in parallel to widelyspaced terminals, so that when in use the current in adjacent elements flows in opposite directions to cancel self-induced fields, and the capacitance is low because of the terminal spac- 6. A resistor especially adapted for high frequency current and with low values of distributed inductance and capacitance, comprising a plurality of thin-walled coplanar sheet resistance elements, and leads connecting them in parallel to widely-spaced terminals, so that when in use the current in adjacent elements flows in opposite directions.

7. A resistor comprising an insulative support, a plurality of sections of thin films of resistance material thereon, and leads connecting them in parallel so that mutual cancellation of self-induced fields occurs when in use, reducing the efiective inductance to a negligible quantity.

8. A resistor comprising a plurality of thinwalled coaxial cylindrical resistance portions for reducing skin-efiect, and leads connecting them in parallel so that rent in adjacent portions flows in opposite directions to effect a mutual cancellation of selfinduced fields, reducing-the efiective inductance to a negligible quantity.

9. A resistor comprising a generally-cylindrical insulative support, a coating of resistance material on the outer surface thereof, a plurality of equally-spaced conductors electrically contacting and dividing said coating into strips of uniform width, and leads connecting alternate when in use the curconductors in parallel, so that when in use the current in adjacent strips flows in opposite directions to cancel self-induced fields.

10. A resistor comprising a hollow cylindrical insulative support, a coating of resistance material on the outer surface thereof, a plurality of uniformly-spaced conductive bands encircling said coated support, thereby connected to and dividing said coating into strips of uniform axial dimension, and leads connecting alternate conductors in parallel, so that when in use the current in adjacent strips flows in opposite directions to cancel self-induced fields.

11. A resistor comprising a hollow cylindrical insulative support, a coating of resistance material on the outer surface thereof, a plurality of conductive bands encircling said coated support, electrically connected to said coating, and uniformly spaced so as to divide said coating into a plurality of elements having equal resistance, leads connecting alternate conductors in parallel, a pair of said conductors being extended, and a hollow cylindrical conductive container enclosing said resistor and to which said extended conductors are supportingly connected, for shielding said resistor from stray electrical fields.

12. A resistor comprising a hollow cylindrical insulative support, an even number of conductive strips equally spaced circumferentially around the outer surface of said support, a resistance coating on said support and electrically connecting said strips, and a pair of leads each connecting alternate strips in parallel, so that when in use the current passing from one lead to another divides to the strips and flows in opposite directions in adjacent coating sections to cancel self-induced fields.

13. A resistor comprising a hollow cylindrical insulative support, an even number of conductive strips equally spaced circumferentially around the outer surface of said support, a resistance coating on said support and electrically connecting said strips, a pair of leads each connecting alternate strips in parallel, and a hollow cylindrical conductive container supportingly enclosing said resistor for shielding it from stray electrical fields.

NORMAN C. FULMER. JULIEN J. MASON.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,552,686 Eversheim Sept.- 8, 1925 2,297,540 Driscoll Sept. 29, 1942 2,392,712 Woodman Jan. 8, 1946 FOREIGN PATENTS Number Country Date 494,331 Germany Mar. 6, 1930 

